W-CDMA is a radio communication interface prescribed in IMT-2000 (International Mobile Telecommunications-2000), and is placed as the most mainstream of radio communication systems. According to W-CDMA, a maximum transmission rate of 384 kbps is used, and therewith, multimedia access such as that of voice, moving pictures, data and so forth is available.
Recently, research and development of radio communication systems called HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access) based on the art of W-CDMA have been proceeding.
FIG. 1 illustrates HSUPA communication. Here, uplink transmission from UE (User Equipment) to a base station is carried out in HSUPA communication. The UE transmits SI (Scheduling Information) to the base station as an uplink data transmission request. In the SI, information concerning transmission data the UE sends is mapped. For example, in the SI, information of “the highest-priority logical channel ID”, “a total amount of data for logical channels”, “a data amount for the highest-priority logical channel” and “transmission power with which the UE can carry out transmission” is mapped. In FIG. 1, BS denotes the base station; the above-mentioned SI denotes an uplink data scheduling request; E-DPCCH denotes uplink control information; E-DPDCH denotes uplink data; E-AGCH denotes highest permitted transmission power; E-RGCH denotes transmission power Up/Down/Hold control; and E-HICH denotes Ack/Nack signal for E-DPDCH.
In the above-mentioned uplink E-DPCCH (E-DCH Dedicated Physical Control Channel), information concerning uplink data is mapped, and E-TFCI (E-DCH Transport Format Combination Indicator), RSN (Retransmission Sequence Number) and Happybit are mapped there.
The base station totals up plural SI items transmitted from the UE, and carries out scheduling to determine transmission timing of the UE that carries out uplink transmission based on communication quality of the UE, a priority of uplink data or such. After carrying out the scheduling, the base station transmits a Grant to the UE as uplink transmission permission. The Grant has two types, i.e., an absolute grant and a relative grant. The absolute grant is transmitted via the above-mentioned downlink E-AGCH (E-DCH Absolute Grant Channel). The base station notifies each UE of highest power that the UE is permitted to transmit. The relative grant is transmitted via the above-mentioned downlink E-RGCH (E-DCH Relative Grant Channel). The base station notifies each UE of whether the UE increases, decreases or holds power to transmit with respect to current transmission power as a signal component of “Up (increase), Down (decrease) or Hold (hold)”.
The UE can carry out high-speed uplink access by transmitting user information to the base station by using an individual channel called E-DCH (Enhanced Dedicated Channel) after being permitted to carry out uplink transmission based on the Grant. In a HSUPA system, retransmission control is carried out the same as that in the HSDPA system, and the UE receives ACK or NACK information for the E-DCH via the above-mentioned downlink E-HICH (E-DCH HARQ Acknowledgement Indicator Channel).
In the HSUPA system, the base station provides instructions to the UE that requests uplink transmission such that reception power of the E-DCH in the base station has a desired throughput by using the signal component of the E-RGCH “Up, Down or Hold” to provide instructions to increase, hold or decrease transmission power. The UE determines the transmission power of the uplink E-DCH according to the “Up, Down or Hold” signal of the E-RGCH. The E-RGCH is transmitted by the base station having been multiplied by a signature pattern that is unique to the E-RGCH. The UE calculates a correlation value between the signature pattern unique to the E-RGCH and the received E-RGCH signal, and thus, determines which one of Commands of Table 1 the E-RGCH is transmitted with:
TABLE 1CommandE-RGCH valueUp+1Hold0Down−1
There, the UE compares the E-RGCH correlation value with a threshold to determine “Up, Down or Hold”. For example, the following E-RGCH signal determining conditions are used:UP: CE-RGCH>ThDOWN: CE-RGCH<−ThHold: −Th≦CE-RGCH≦Th
CE-RGCH denotes the correlation value between the received E-RGCH and the E-RGCH signature pattern. Th denotes the threshold for E-RGCH. The threshold Th is set, for example, to be an appropriate value based on an experiment or such before the shipment of a mobile terminal.